I've known kids through childcare who would do it. Two urinators, one vomiter. One of the urinating kids would stand on top of something and wee everywhere. The other would get within eyesight of an adult, then say "I'm doing a wee" and then wee. Both were attention deprived at home.

The vomiter was about two. Cried til she vomited once, and was sent home. Not sure if she figured it out or if she just escalated very quickly, but if she disagreed with something (like not being able to have another kid's drink) she would cry and vomit within a minute. She ate heaps of dairy too, so it was gross. It was the speed with which it escalated and he trivial nature of what she would do it over - didn't happen at drop off, for example, that made us think it was defiance. Or frustration, or whatever. We used to just clean it up and get on with life, and eventually she stopped.

Someone told me about 123 Magic once. I tried counting to 3, or 5 or 10 before we did things, and my DD1 would get so excited about counting that she would just do whatever it was I asked. So that bit was kinda magic. Never had to go any further.